Objective for photographic and like purposes



L. B. BOOTH.

OBJECTIVE FOR PHOTOGRAPHIC AND LIKE PURPOSES.

APPLICATION FILED Nov. 9, 1920.

1,421,156. Patented June 27, 1922.

The. front air-space has thus the UNITED STATES PATENT ounce.

LIONEL BARTON BOOTH, OI CAMBRIDGE, ENGLAND.

OBJECTIVE FOR PKOTOGRAPHIC AND LIKE PURPOSES.

Application filed November 9, 1520. Serial No. 422,900. I

To all whom it may concern:

Be it known that I, LIONEL BARTON Boom, a subject of the King of GreatBritain, residing in Cambridge, England, have invented certain new anduseful Improvements in Objectives for Photographic and like Purposes, ofwhich the following is a specification.

The aim or" this invention is to produce an objective corrected forspherical aberration coma, curvature, astigmatism and chromaticaberrations for a very large aperture.

Many objectives have been made which a positive lens of glass with highrefractive index is followed by an air-space and then by a negative lenswith a lower or nearly equal refractive index, following which is anair-space and then a cemented component consisting of a dispersive lensof glass with low refractive index cemented a coilective lens of giasswith high; retract ind-en. of a dispersive -ens and cemented surfaceback has collective power. By obtaining positive power from theoementedsurface, less curvature other surfaces of the system to obtain the samefocal length and therefore the tenet ency is to reduce sphericalaberration and to render a large aperture possible; in addition such anarrangement tends to reduce the Petzval sum on which the curvature offield to a large extent depends. in this invention it is proposed touse, instead of the simple lens for the first positive lens, a cementedpair similar to the last component i. e. to make an objective consistingof:

(1) A front component consisting of a positive lens made of crown glassof high refractive index in the vicinity of 1.6 or 1.61 and having lowdispersion, cemented to a negative lens of flint glass of not greaterrefractive index, the former leading and being bi-convex.

(2) A middle component consisting of a. bi-concave negative lens of aflint glass of refractive index less by at least .04 than that of thecrown glass used in the positive lenses the front component butreversed, i. e. with the dispersive lens towards the front, the glassesbeing similar to but not necessarily is required on some of theidentical with those used in the front component.

The curves and separations can be determined by calculation so as toproduce an obj ective remarkably free from the usual aberrations owingto the shallowness oi the curves resulting from the considerablecontribution to the power of the system bv the two cemented surfaces ofpositive pbwer. A diaphragm may be placed in either of the air-spacesaccording to convemence.

Full details are now given of an obiectiveconstructed on the principleslaid ddwn above. The negative lenses are *oretera-biv, indicated, oi thesame glass. Where the sin; preceding radius is the surface is vex andwhere concave to the incident light, the surfaces being numbered orderin which they occur, beginning that on which the light first fails2- JCentral I +2 6 v thickness. S,T;= 3 M;- .lJ .l. l:- i611 ,kTz 2Lgp3} 1.;

(cemented) fifi 7 n,-2nd lens .1 2.18

separation .52 f 1 r.,= -23; in, did lens H5=+23 .i 1.9

Air separatio.-= .53 T r 52 a l v s, 4th lens 1 ice I (cemented) I. It-5th lens f g- :51 49 1.95

p flu/lui 5 Glasses used: L, and L5 o 1.6109 1.62411 L, L, and L 1.54851.56424 F=6 Clear aperture 2.08 Relative aperture /3.

Having thus described the nature of the said invention and thebest'means I know of carrying the same into practical effect, I claim 1.An objective corrected for spherical aberration, coma, astigmatism andcurvature, as well as for chromatic aberrations capable of being madewith a very large relative aperture made up of (1) a front componentconsisting of a positive lens made of crown glass of high refractiveindex in the vicinity of 1.6 or 1.61 and having low dis persion,cemented to a negative lens of flint lass of not" greater refractiveindex the ormer leadingand being bi-co-nvex; (2) a middle componentconsisting of a lei-concave negative lensof a flint has of refractivein- 5 dex less b at least .04 an thatv of the crown glass use in theositive lenses of the system and having a d1s sion at least as eat asthat of either oFthe flint glasses use for the other dispersive lensesof the system;

10 (3) a back component, similar in type to the v front component butreversed, that is, With the dispersive lens towards the front, theglasses bein in type similar to but not necessarily identicalwith'those'used in the front oomponent, substantially as described.

2. An objective as claimed in 'claim 1 "wherein the negative-lensesinthe several components are all of thesame glass.

In testimony whereof 'I have signed my name to this specification.

LIONEL BARTON BOOTH" v

